The goal of the tensegrity project is to investigate the possibility of using a tensegrity structure in space exploration. This year's team is responsible for building and testing models which can be used to validate the current computer models. A validated model will allow the team to efficiently change various paramaters of the structure to obtain the best possible model. Upon validating the computer model, the physical model will be tested to failure.

Background

A tensegrity structure is one in which all members of the structure are in either pure tension or compression. By eliminating any bending the strength to weight ratio increases greatly. The idea became greatly popularized by an artist by the name of Kenneth Snelson who was also responsible for giving the structure it's name.

Project Background

The 2013-2014 Design Senior Design Team is the third team to continue the development of this project. Previous teams were responsible for choosing a specific structure and investigating the possibility of using strings and motors to create a mobile structure. By adjusting string lengths the round structure can be made to "walk". This will allow for a single structure to be responsible for landing on and exploration of Titan.

Design Goals

Validate the computer model

Build a prototype that can survive a drop from 10 meters with a payload of 5 kilograms

Acquire stress data in each cable and strut of the structure

5 kg payload experiences an acceleration of less than 25G’s when dropped from 10 meters

Manipulate the landing orientation of the structure to land in one of the best orientations

Refine the design of the structure so that it has a payload to weight ratio of 2.33 to 1

Provide slow motion videos of deforming and failing components

Acquire enough data to provide a model simulation of a structure with a 75 kg payload

Design Specifications

Problem Statement

The goal of this project is to create a system able to attenuate impact forces on a tensegrity structure's payload as it is put through tests analogous to a a passive descent and landing on Titan. The team will construct the fully instrumented 6-bar Icosahedron containing a minimum 5 kg payload and test to the point of failure. Data acquired form the physical tests will be used to validate an analytic model which can then be used to design a structure capable of a much larger 70 kg payload. This will support the research being done at the Intelligent Robotics Group (ORG) regarding the Super Ball Bot tensegrity.

Target Specifications

Engineering Specification Targets

Specific Requirements

Description

Acceptable

Target

Build Prototype Structure

Build a prototype structure that has a payload and sensors to acquire stress in each component and acceleration of the payload

Have prototype built with a 5kg payload that is able to drop from 10 meters

Have prototype built where the payload can be exchanged for heavier weights than 5kg and can be dropped from more than 10 meters

Stress

A major goal is to drop test this tensegrity structure and be able to acquire stress data for each strut and cable

Acquire stress from 36 load cells for each drop and understand stress behavior in the tensegrity structure

Payload Acceleration

A payload on the tensegrity structure will experience a rapid acceleration upon impact from drop tests.

Attach an accelerometer to the payload and acquire data showing that the payload experiences accelerations approaching 25G’s or less

Acquire acceleration data that shows that a 5kg payload on our tensegrity structure will experience less than a 25G acceleration when dropped from at least 10 meters

Manipulation of Orientation

By manipulating how the tensegrity structure falls we can change how the structure falls

Be able to control the drop of the structure to manipulate how it lands

Be able to control the structure so that it lands in the best possibly orientation every drop

Weight to Payload Ratio

Good engineering structure designs in the aerospace industry will weigh less than the payload they can carry by some ratio

Understand a starting payload to weight ratio for this structure and get the structure weight below the payload weight

Refine the structure design so that the payload to weight ratio is 2.33 to 1

Videos of Drop Tests

When preforming drop tests we will be taking videos of each test to get a visual of impact

Have multiple videos of drop tests to present to NASA

Have slow motion videos that show impact deformation and components failing catastrophically

Acquire Data

Need to get as much data as possible from the tensegrity structure regarding stress in each member or string and acceleration of payload

Acquire enough data to have a significant impact on the understanding of tensegrity structures and how they work

Acquire enough data to prove out a mathematical model of tensegrity structure with 75kg payload

Project Learning

Major Results of Project Learning - Our project was continued from previous senior design projects. Because of this, much of our project learning consisted of becoming familiar with prior teams' knowledge.

Recording data is our main goal - all data is good data

The six-strut tensegrity structure is the most stable

We need six strings in the middle to support the payload

Background Research

Initial Interviews

Concept Development

Concept Development Table

Problem Task

Possible Solutions

Cables

200 lb test string

1200 lb paracord

550 lb paracord

Shock cord

Connection Methods

Knots

Snap Swivels

Key Rings

Stress Data Acquisition

Strain Gauges

Purchase Load Cells

Manufacture Load Cells

Stress Sensors

Acceleration Data Acquisition

3-Axis Accelerometer

3-Axis/Gyro Accelerometer

Single Axis Accelerometer

Data Acquisition Board

Arduino Duo

Arduino Mega

Raspberry Pi

Beagle Bone

Board from Measurement Computing.com

Data Acquisition Software

Matlab

Python

Linux

Data Storage Methods

USB tether to computer

Wireless

PCI Card

Cat 5 tether to computer

USB storage

Micro SD Card

Concept Testing

Cable Testing

We chose to test the spring constants of Shockcord and 550 Paracord. These are the results obtained:

Drop Tests

Our drop tests indicate that we are seeing a G-force of 25-30 when dropped from a height of 1 meter, a G-force of 35-40 when dropped from a height of 1.5 meters and a G-force of 40-50 when dropped from a height of 2 meters. The table shows a single drop test from each height. Multiple tests were completed to verify the results.

Structure Design

Structure Assembly

Assembly of Outer Structure

Full Assembly with Payload

Second Iteration

We chose to use paracord for the outer structure and a spring/paracord combination to support the payload. The inner support system was designed in such a way that we can change out the springs. This allows us to increase the weight of the payload which lets us gather more data without extensive redesign of the structure.

The final design of this year's tensegrity model

The spring/paracord design for supporting the payload

The Payload

Team Members

The current team is composed of four undergraduate mechanical engineering students and two graduate mechanical engineering students.

Picture

Bio

Discipline

Alex Ackerman

Alex Ackerman is a senior in Mechanical Engineering at the University of Idaho. He has been interested in mechanics ever since he was a kid and is particularly interested in its application for motor vehicles. In addition to being a student he is also a member of the Naval ROTC program. Upon graduation he hopes to pursue a career as a Navy SEAL or Navy Explosive Ordinance Disposal (EOD) Technician.

ME

Nick Clyde

Nick is a senior Mechanical Engineering student and has taken an interest in fluids and thermodynamics. Nick had an internship last summer at ATK in Lewiston, Idaho. He will start his engineering career at ConAgra Foods/Lamb Weston in June and later continue his education by pursuing a Masters of Science in a Mechanical Engineering field. His hobbies include hunting, shooting sports, snowmobiling, water sports such as wake-boarding and anything that keeps him active and outdoors.

ME

Will Hoffman

Will Hoffman is a senior studying mechanical engineering. He loves space and all of the sciences pertaining to space exploration, so this has been a really fun project for him. After he graduates, he will probably go to graduate school to further develop in his infinite quest for knowledge.

ME

Brenden Kaschmitter

Brenden Kaschmitter is a senior studying mechanical engineering with a minor in material science engineering. He will graduate in the Fall of 2014. He chose mechanical engineering for an interest in how things worked. Upon graduation he would like to pursue a career in aeronautics or nuclear power. He likes to spend his free time outdoors hiking, skiing, and rafting.

ME

Mary Yovanoff

Mary Yovanoff is senior in mechanical engineering. She is interested in designing toys to teach kids about engineering. She plans on returning to school in a year or two to pursue a masters degree in Human Factors. When she graduates, Mary will also have her bachelors degree in Psychology. In her free time she likes swimming, reading, being outside and working with little kids.